1. Field of the Invention
The present invention relates to an OLED (organic light-emitting device) panel obtained by forming an OLED on a substrate and sealing the OLED between the substrate and a cover member. The invention also relates to an OLED module in which an IC including a controller, or the like, is mounted to the OLED panel. In this specification, xe2x80x98light-emitting devicexe2x80x99 is the generic term for the OLED panel and for the OLED module. Electronic equipment using the light-emitting device is also included in the present invention.
2. Description of the Related Art
Being self-luminous, OLEDs eliminate the need for a backlight that is necessary in liquid crystal display devices (LCDs) and thus make it easy to manufacture thinner devices. Also, the self-luminous OLEDs are high in visibility and have no limit in terms of viewing angle. These are the reasons for attention that light-emitting devices using the OLEDs are receiving in recent years as display devices to replace CRTs and LCDs.
An OLED has a layer containing an organic compound (organic light-emitting material) that provides luminescence (electroluminescence) when an electric field is applied (the layer is hereinafter referred to as organic light-emitting layer), in addition to an anode layer and a cathode layer. Luminescence obtained from organic compounds is classified into light emission upon return to the base state from singlet excitation (fluorescence) and light emission upon return to the base state from triplet excitation (phosphorescence). A light-emitting device according to the present invention can use one or both types of the light emission.
In this specification, all the layers that are provided between an anode and a cathode together make an organic light emitting layer. Specifically, the organic light emitting layer includes a light emitting layer, a hole injection layer, an electron injection layer, a hole transporting layer, an electron transporting layer, etc. A basic structure of an OLED is a laminate of an anode, a light emitting layer, and a cathode layered in this order. The basic structure can be modified into a laminate of an anode, a hole injection layer, a light emitting layer, and a cathode layered in this order, or a laminate of an anode, a hole injection layer, a light emitting layer, an electron transporting layer, and a cathode layered in this order.
The problem in putting a light-emitting device using the OLED into practice is degradation of the device by heat, light, moisture, oxygen, and other causes.
When manufacturing a light-emitting device with OLED, in general, the OLED is formed after a wiring line and a semiconductor element are formed in a pixel portion. Once the OLED is formed, a first substrate on which the OLED is placed is bonded to a second substrate (made of metal or glass) for sealing (packaging) the OLED so that the OLED is not exposed to the outside air. A resin or the like is used to bond the substrates and nitrogen or inert gas fills the space between the substrates. However, oxygen easily reaches the OLED sealed as above by the substrates and a resin through the slightest crack in the package. Furthermore, moisture finds no difficulty in seeping into the OLED through the resin used in bonding and sealing. This causes non-light emission portions called dark spots, which grow larger with time and emit no light, which becomes a problem.
The present invention has been made to solve the above problem and an object of the present invention is therefore to provide a light-emitting device using a highly reliable OLED. Another object of the present invention is to provide electronic equipment with a highly reliable display unit by employing such light-emitting device with the OLED for its display unit.
The present invention relates to a technique for sealing an OLED that is placed on a substrate having an insulating surface. To seal the OLED, the present invention employs vacuum sealing using a film that is provided, on one side (inside) at least, with a thin film low in gas transmissivity (typically, a thin film mainly containing carbon, a silicon oxynitride film, a silicon nitride film, a film of a compound expressed as AlNXOY, a AlN film, or a laminate of these films).
In the present invention, a film low in gas transmissivity is used to provide a film while adding a rare gas element to reaction gas in order to give the film flexibility. The present invention is characterized in that a thin film low in gas transmissivity (typically, a thin film mainly containing carbon, a silicon oxynitride film, a silicon nitride film, a film of a compound expressed as AlNXOY, a AlN film, or a laminate of these films) contains a rare gas element to ease the internal stress in the film and to make the film flexible, and that a film provided, at least on one side (inside), with the thin film is used to vacuum-seal a light-emitting device having an OLED.
A film obtains flexibility by containing rare gas. Therefore, the thin film used to provide the wrapping film is prevented from developing a crack or peeling off when thermally press-fit in vacuum. Moreover, the film used as a lining can improve the heat resistance and mechanical strength of the wrapping film.
A structure of the present invention disclosed in this specification is a light-emitting device characterized in that:
the device includes a TFT, an active matrix substrate on which a light emitting element having the TFT is formed, a desiccant, and a protective unit wrapping the active matrix substrate; and
the protective unit is a film at least partially provided with a thin film that contains a rare gas element and mainly contains carbon. In this specification, a substrate on which an OLED is formed is called an active matrix substrate.
In the above structure, the light emitting element has an anode, a cathode, and an EL material sandwiched between the anode and the cathode.
In the above structure, the protective unit is brought into contact with the active matrix substrate by vacuum press-fitting. Accordingly, the protective unit has flexibility to a certain degree. Any film can be used for this protective unit as long as it is an excellent gas barrier and is transparent or translucent with respect to visible light. For example, the protective unit may be a film entirely covered with a thin film that contains carbon as its main component, or a film provided with a thin film that contains carbon as its main component on one side (inside or outside).
The present invention is characterized in that the thin film that contains carbon as its main component is a DLC (diamond like carbon) film with a thickness of 3 to 50 nm. A DLC film has a SP3 bond as the bond between carbon atoms in terms of short range order. Macroscopically, a DLC film has an amorphous structure. A DLC film is composed of 70 to 95 atomic % of carbon and 5 to 30 atomic % of hydrogen, which makes the DLC film very hard and excellent in insulating. A DLC film as such is also characterized by having a low transmissivity for steam, oxygen, and other gas. A DLC film is known to have a hardness of 15 to 25 GPa when measured by a microhardness tester.
A DLC film is formed by plasma CVD, microwave CVD, electron cyclotron resonance (ECR) CVD, sputtering, etc. Any of these methods can provide a DLC film having an appropriate adhesion. A DLC film is formed by setting a substrate as the cathode. When a negative bias is applied and some of ion impact is utilized, a dense and hard DLC film can be obtained.
Reaction gas used in forming a DLC film by plasma CVD is hydrocarbon-based gas, for example, CH4, C2H2, or C6H6. The reaction gas is ionized by glow discharge and the ions are accelerated to impact against a cathode to which a negative self-bias is applied. As a result, a dense and flat DLC film can be obtained.
This DLC film is characterized by being an insulating film which is transparent or translucent to visible light.
In this specification, being transparent to visible light means to have a transmissivity of 80 to 100% for visible light whereas being translucent to visible light means to have a transmissivity of 50 to 80% for visible light.
A silicon oxynitride film may be used instead of the above DLC film. In this case, the protective unit is a film at least partially provided with a silicon oxynitride film.
A silicon nitride film may be used instead of the above DLC film. In this case, the protective unit is a film at least partially provided with a silicon nitride film.
An AlN film may be used instead of the above DLC film. In this case, the protective unit is a film at least partially provided with an AlN film.
An AlNXOY film may be used instead of the above DLC film. In this case, the protective unit is a film at least partially provided with an AlNXOY film.
A laminate having in combination a DLC film, a silicon oxynitride film, a silicon nitride film, an AlN film, and a film of an AlNXOY film may also be used. In this case, the protective unit is a film at least partially provided with the laminate.
Preferably, the silicon nitride film, the AlN film, or the AlNXOY film is formed by sputtering and rare gas is introduced to the chamber so that the formed film contains a rare gas element (typically Ar) in a concentration of 0.1 atomic % or higher, more desirably, 1 to 30 atomic % or higher.
In the above structure, a desiccant is preferably placed between the active matrix substrate and the protective unit sealed in vacuum in order to prevent degradation of the light emitting element. A suitable desiccant is barium oxide, a calcium oxide, silica gel, or the like. The desiccant is placed before or after a flexible printed substrate is bonded. Alternatively, the desiccant may be set in a flexible film of the flexible printed substrate and then the flexible printed substrate is bonded. Preferably, the desiccant is placed near the location where the protective unit is press-fit in vacuum.
A structure of the present invention for obtaining the above structure is a method of manufacturing a light-emitting device, characterized by comprising the steps of:
forming a light emitting element on a substrate that has an insulating surface;
bonding a flexible printed substrate to the edge of the substrate; and
sealing in vacuum the light emitting element and a part of the flexible printed substrate using a film that is covered with a thin film mainly containing carbon.
In the above structure, the step of forming the light emitting element may be followed by a step of thinning the thickness of the substrate. If the substrate is thinned, the thinning step is preferably followed by the step of bonding the flexible printed substrate to the edge of the former substrate.
In the above structures, the method is characterized by comprising a step of placing a desiccant that is in contact with the flexible printed substrate before the vacuum sealing step. The vacuum sealing step employs thermal press-fitting.
In the above structures, the thin film mainly containing carbon is a DLC film containing a rare gas element in a concentration of 0.1 atomic % or higher, preferably 1 to 30 atomic %.
In the above structures, the rare gas element is one or more kinds of elements selected from the group consisting of He, Ne, Ar, Kr, and Xe.